It is known to locate a drilling machine at an upper level and use it for first drilling a small pilot hole on a single downward pass, followed by an enlargement of the pilot hole in a single upward pass. Such a machine is disclosed by U.S. Pat. No. 3,220,494, granted Nov. 30, 1965, to Robert E. Cannon, Douglas F. Winberg, Dean K. McCurdy and Richard J. Robbins.
It is also known to use a drilling machine located at an upper level to bore a large diameter hole in a single downward pass. Examples of this type of equipment are disclosed by U.S. Pat. No. 3,383,946, granted May 21, 1968, to Carl L. Lichte and William M. Conn; by U.S. Pat. No. 3,648,788, granted Mar. 14, 1972, to John R. McKinney; by U.S. Pat. No. 3,762,486, granted Oct. 2, 1973, to William W. Grovengurg and Robert R. Gatliff.
The following patents disclose several types of known (at least in the patent literature) expandable reamers:
U.S. Pat. No. 1,317,192, granted Sept. 30, 1919, to Arthur S. Jones; U.S. Pat. No. 1,402,786, granted Jan. 10, 1922 to W. F. Muehl; U.S. Pat. No. 1,498,463, granted Oct. 26, 1922 to J. P. McCloskey et al; U.S. Pat. No. 1,499,938 granted July 1, 1924 to R. Leedom; U.S. Pat. No. 1,561,523 granted Nov. 17, 1925 to A. W. Riedle; U.S. Pat. No. 1,618,294, granted Feb. 22, 1927 to J. Olson; U.S. Pat. No. 2,139,323 granted Dec. 6, 1938 to E. H. Zum-Berge; U.S. Pat. No. 2,799,475, granted July 16, 1957 to D. L. Harlan et al; U.S. Pat. No. 2,868,510, granted Jan. 13, 1959 to C. A. Dean; U.S. Pat. No. 3,112,802, granted Dec. 3, 1963 to G. W. Amann et al; U.S. Pat. No. 3,757,876, granted Sept. 11, 1973 to Robert L. Pereau; and Canadian Pat. No. 632,051, granted July 4, 1961, to Austen M. Shook.